1. Technical Field
The present disclosure relates to a semiconductor laser driver and an image forming apparatus incorporating same, and more particularly, a semiconductor laser driver capable of controlling multiple semiconductor lasers such that light-emission intensities of the multiple semiconductor lasers become predetermined light-emission intensities.
2. Description of the Background Art
Recently, semiconductor laser diodes have come to be widely used in a variety of types of electrical equipment, for example, laser printers, optical disk apparatuses, fiber-optic communication apparatuses, and mobile phones, because of their compact size, low cost, and ease of use.
However, the current/light-emission intensity characteristics of the semiconductor laser diode are dependent on temperature. Accordingly, it is necessary to control light-emission intensity to obtain a predetermined light-emission intensity reliably. This light-emission intensity control is called Automatic Power Control (APC). In the APC process, before the semiconductor laser diode is actually driven, the laser diode is driven in advance, a quantity of light output from the laser diode is received by a photodiode (PD), and the detection current values of corresponding quantities of light are stored in a storage device. Then, the laser diode is controlled using the current values saved in the storage device so as to obtain a desired light-emission intensity reliably.
APC is executed by an APC signal output from an image controller that is a previous stage of the semiconductor laser driver. The semiconductor laser driver is contained in a small unit, for example, a so-called laser scanner unit, and is often positioned away from the image controller. The APC signal from the image controller is transmitted to a substrate of the semiconductor laser driver in the laser scanner unit through wiring such as harness.
Heretofore, a single semiconductor laser is controlled by a single APC line. Consequently, the number of APC signal lines increases as the number of semiconductor lasers is increased.
In order to address this problem, several techniques have been proposed. In one example proposed in JP-H11-348342-A, by using a single S/H signal (APC signal) for multiple semiconductor lasers, APC is executed for the semiconductor laser connected to the S/H signal and the image data signal whose states are enabled. Thus, the number of APC signal lines can be reduced. However, this configuration necessitates complicated timing control between the APC signal and the image data signal. Therefore, as the number of semiconductor lasers is increased, control becomes more difficult.
In another example proposed in JP-2007-021826-A, the number of control signals is minimized and a state-machine control circuit at the semiconductor laser driver side executes APC control of the semiconductor lasers. However, although the number of control signals can be reduced by providing state-machine control circuit at the semiconductor laser driver side, such a configuration is complicated and costly because the size of the circuit and substrate area occupied increases.